The present invention relates to a cylinder head gasket sandwiched between a cylinder head and a cylinder block of an open deck type engine for sealing.
A cylinder head gasket is tightened by head bolts and sandwiched between engine members such as a cylinder head, a cylinder block (cylinder body) or the like, of an automobile engine for sealing fluids such as combustion gas, oil, coolant or the like.
On the other hand, an engine can be distinguished based on a form of a cylinder block into a closed type engine having no coolant passage at a contact surface of a cylinder head at a cylinder block, and an open deck type engine having a contact surface which is open as a coolant passage of a cylinder head at a cylinder block. As shown in FIG. 10, the open deck type engine includes a coolant passage (water jacket) 62 at a portion close to a cylinder head of an engine block 60, and is advantageous in terms of a cooling ability and a reduction in weight thereof. In addition, it is easy to produce the open deck type engine because of an opening portion therein.
Regarding a cylinder head gasket for the open deck type engine, a metal gasket has been provided with a grommet along an inner periphery of a cylinder hole in a base plate to be inserted to bridge a cylinder portion of a cylinder block and an outer wall portion forming an outer side of a coolant passage. The thickest portion of the grommet formed at the inner side of a cylinder sleeve seals combustion gas of a cylinder bore. Also, step beads formed on both sides of the coolant passage seal the coolant (For example, refer to Japanese Patent Document 1: Japanese Patent Publication No. H10-281290).
In the cylinder head gasket, the step beads are provided for sealing the coolant between the coolant passage and the cylinder bore. The step beads have a portion thicker at an inner periphery side and a portion thinner at an outer periphery side on an upper surface of an inner cylindrical portion of the cylinder block. Therefore, when a large pressing force is applied to the step beads, a large surface pressure is applied to the inner periphery side, thereby making the pressing force difficult to be optimized. In addition, a moment, inclining toward inner side, acts on the upper portion of the inner cylindrical portion, thereby deforming the cylinder bore.
The present invention has been made to solve the above-mentioned problems and provides a cylinder head gasket to be used for an open deck type engine. The cylinder head gasket adjusts a surface pressure on an upper surface of a cylinder portion forming a cylinder bore of a cylinder block, thereby reducing deformation of the cylinder bore and preventing the cylinder bore from buckling.
Further objects and advantages of the invention will be apparent from the following description of the invention.